In many instances it is necessary to provide housing structures adapted to enclose electrical elements, circuitry, devices, or appliances so as to exclude aggressive substances and media, e.g. corrosive atmospheres, agents and substances which might otherwise interfere with the proper functioning of the electrical device or mechanical appliance.
The housing can be composed of two parts which are fixed together with interposition of a seal and which can be composed of materials inherently resistant to attack by aggressive substances, generally synthetic resins or plastics. The housing members may be provided with engaging or interfitting elements to assist in sealing or joining them together and, for example, one of the two housing portions can be provided with an apron forming a socket in which the rim of the other housing member is received.
Plastic housings of the aforedescribed type have, while providing a sealed chamber, been found to have certain problems. For example, difficulties have been encountered in mounting the electrical devices or units in the housing since the thin-wall structure is frequently overloaded by the weight of the electrical devices and/or the stresses applied by bolts or other fasteners used to secure the devices in place. While an ostensibly simple solution is to increase the wall thickness, this has been found to be uneconomical and to increase the material cost because in some instances the added thicknesses of material is unnecessary. Furthermore, simply increasing the wall thickness results in an increased weight which makes the housing difficult to handle, manipulate and emplace. Another disadvantage of the earlier systems is that they frequently required inordinate amounts of space for transport and storage.